The structures, geometries, energy transfer dynamics and excited state energies of photosynthetic carotenoids will be studied in native and crystallized pigment-protein complexes. The specific aims of the proposed research are to: (1) Determine the configuration of the carotenoids in the pigment-protein complexes of photosynthetic bacteria; (2) Determine the mechanism of carotenoid-to-bacteriochlorophyll energy transfer in antenna complexes of photosynthetic bacteria; (3) Determine the nature of the association of carotenoids with the protein and bacteriochlorophylls in photosynthetic pigment-protein complexes. The approach will be to use various optical spectroscopic techniques as probes of the various preparations. The results are important because the survival of photosynthetic organisms depends on the ability of these systems to utilize efficiently their absorbed energy and to protect themselves from photooxidative destruction. Carotenoids perform these functions.